Supports or props for holding the boom arm or arms on a material handling vehicle in an elevated position have been in use for some time. The most common means utilized on these material handling vehicles which rely upon the extension of hydraulic cylinder or cylinders to raise the boom arms is to simply clamp a piece of angle iron, of proper length to span the distance between the end of the cylinder and the boom, to the extended rod of at least one of the boom cylinders. The angle iron, being in contact with both the rod end of the cylinder and the boom arm, will physically prevent the collapse of the boom cylinders, even if the hydraulic fluid is exhausted from the head end of the boom cylinders. However, such a means requires the installation and removal of the clamps to be performed while the boom arms are in an elevated position, which is awkward at best and with larger loaders require some auxially support, such as the ladder, for the workman installing or removing the angle iron. Such an arrangement is also undesirable because the elements of the prop or support are separable from, and are not intrinsically carried by the vehicle. Storage of the clamps and angle iron piece then becomes a nuisance.
Another type of known boom prop or support, such as that shown in U.S. Pat. No. 3,918,601 issued November 1975 to R. F. Zimmerman, supports the boom arms by locking the implement linkage. Such supports however, have application only to those types of vehicles which utilize a four-bar linkage or some modification thereof, to actuate the implement. Still other types of boom props have required the pinning of a structural member between the vehicle and the boom. Alignment of the holes with such arrangements are necessary and dictate the proper coordination of an operator in the vehicle cab, who is controlling the vertical elevation of the boom, with another workman who must insert a pin when the holes in the prop and the boom arm are aligned.
Another type of boom prop, such as that shown in U.S. Pat. No. 3,995,761 issued Dec. 7, 1976, function by physically blocking a linkage to which the boom arms are pivoted. This arrangement overcomes most of the aforementioned disadvantages, but is not applicable to the conventional commercial loader in which the boom arms are pivoted directly to the vehicle.
It is therefore an object of this invention to provide a boom prop for a conventional loader which is simple, which may be rendered operative or stored by one individual, and which positively limits downward movement of elevated boom arms but does not restrict the upward movement of the boom arms above the limit of the downward movement.